Method of polymerization of styrene



Patented Nov. 28, 1939 METHOD 0F POLYMERIZATIGN (NF STYRENE Norman D.Scott, Sanborn, N. Y., assignor to E. I. du Pont dc Nemours & Company,Wilmington, Did, a corporation of Delaware No Drawing. Originalapplication December 10,

1935, Serial No. 53,756. Divided and this application February 1, 1938,Serial No. 188,194.

2 Claims.

This invention relates to an improved method for polymerizinghydrocarbons.

This application is a division of my copending I application S. N.53,756, filed December 10, 1935, which is a continuation-in-part ofapplication Serial Number 726,569, filed May 19, 1934, which has issuedas U. S. Patent 2,048,169.

An object of the present invention is to provide novel andimprovedmethods for polymerizing unsaturated hydrocarbons to produce avariety of useful polymerized substances, as hereinafter described.Further specific objects will be apparent from the following disclosure.

4 I have found that the addition compounds formed by the reaction ofalkali metals with polycyclic aromatic hydrocarbons such as naphthalene,diphenyl and phenanthrene, and the like, have decided advantages ashydrocarbon'polymerizing agents in that they are easily prepared, can behandled as solutions, do not ignite in contact with air under ordinaryconditions, do not elvolve hydrogen or ignite on contact with water, yetin general are more efiective than the free alkali metals aspolymerizing agents. Certain methods of forming these addition compoundsare disclosed and claimed in my copending applications Serial Numbers638,524 and 678,261, filed Oct. 19, 193.2 and June 29, 1933,respectively, which have been issued as U. S. Patents 2,027,000 and2,123,793, respectively. One convenient method is to dissolve sodium ina solution of naphthalene or other polycyclic aromatic hydrocarbon inliquid dimethylether at a temperature somewhat below -24 0., whilestirring or abrading the sodium in contact with I the mixture to startthe reaction. When the reaction is once started, the solution becomeshighly colored and solution of the metal occurs at a rapid rate. Theamount of sodium readily dissolved will range in general from one to twogram atoms per gram molecule of the aromatic hydrocarbon. Various otheraliphatic ethers may be used as solvents in place of dimethyl ether, asfor example, methyl ethyl ether, poly ethers such as dimethyl or diethylglycol ethers, or cyclic ethers such as dioxane.

When the solution of the sodium hydrocarbon compound or mixture ofcompounds has been prepared, it either may be mixed with the hydrocarbonto be polymerized, or as is usually preferable to avoid wasting solvent,the methyl ether or other special solvent used in preparing the sodiumcompound may be partly distilled off and recovered before contacting thesodium compound with the hydrocarbon. In the latter case,

(cif zoo-n1) it is advisable to leave a small amount of the solventether in contact with the sodium compound, e. g., equivalent to around20% by weight of the compound, as this increases the stability of thesodium compound.

I have discovered that the herein described addition compounds of alkalimetals and polycyclic aromatic hydrocarbons have a marked polymerizingefiect when contacted with an unsaturated hydrocarbon which does notreadily form sub- 3@ stitution compounds of the alkali metals and whichhas conjugated double bonds, at least one of the conjugated double bondsoccurring in an aliphatic radical. Further, I have found that theseaddition compounds have little or no polymerizing effect on unsaturatedhydrocarbons which do not have conjugated double bonds as describedabove. Examples of hydrocarbons with conjugated unsaturation which maybe readily polymerized by treatment with small 9 amounts of the alkaliaddition compounds are butadiene, isoprene, dimethyl butadiene, styrene,cyclopentadiene, and 1,2-dihydronaphthalene.

My invention is not limited to these examples, as other unsaturatedhydrocarbons of the class mentioned above, as well as their substitutionderivatives, may likewise be polymerized by the method of the presentinvention. Also, my method may be applied to various products containingone or more of such unsaturated hydrocarbons, e. g., crude gasoline orother petroleum fractions.

The polymerizing action is rapid and complete, even at relatively lowtemperatures, e. g., 20 to 302. C. Alkali metals are known to causepolymerization of unsaturated compounds, but my herein described alkalimetal addition compounds diifer from the alkali metals in that theycause more rapid and more complete polymerization of the conjugatedunsaturates than do alkali metals. For example, a small amount of anether solution of the sodium naphthalene addition compound added to1,2-dihydronaphthalene at 20 to 30 C. rapidly and substantially com- 4550 I have found that the herein described alkali metal additioncompounds are selective in their polymerizing action in that theyreadily polymerize the conjugated unsaturates, while havingsubstantially no polymerizing action on non- 55 conjugated unsaturates,e. g.,v amylene or limonene.

The selective polymerizing action of the herein described alkali metaladdition compounds is illustrated by the fact that whereas the sodiumnaphthalene compound causes rapid polymerization of butadiene, it hassubstantially no action on amylene.

My novel polymerizing agents may be contacted with the hydrocarbon to bepolymerized by various methods, which will be apparent to those skilledin this art. I prefer to first dissolve the unsaturated hydrocarbon tobe polyermized in a solvent ether of the type suitable for the formationof the alkali metal addition compound, as described above (e. g.,dimethyl ethylene glycol ether) and then add a small amount of thealkali metal addition compound' or an ether solution of the same.

The amount of the alkali metal hydrocarbon compound required will varyover a wide range, depending upon the temperature, time of contact, thenature and amounts of impurities in the hydrocarbon, and the degree ofpolymerization desired. Only small amounts of the addition compound willbe required, for example, 1-10% of the weight of the compound to bepolymerized. Ordinarily, a mere trace of the addition compound issufficient to effectively polymerize the unsaturated compound; ifmoisture or other impurities with which the addition compound will reactare present, a correspondingly .larger amount of the addition compoundmust be added.

The polymerization will occur within a wide range of temperatures,including temperatures both below and above ordinary room temperature.For example, I have polymerized unsaturated hydrocarbons in accordancewith the" herein described invention at temperatures as low as 60 C.,and also at relatively high temperatures, e. g., 50 to 60 C. PreferablyI operate at temperatures below the boiling point of the solventemployed. Generally, the physical properties of the polymer will vary,depending on the temperature employed, the higher temperatures favoringthe formation of polymers of lower molecular weights and lower meltingpoints. The polymers formed by my process are resinous in nature andvary from viscous, oily liquids to hard, brittle solids. The polymerizedproduct may be recovered by removing solvent and unpolymerizedhydrocarbons by means obvious to the skilled chemist. For example, thereaction mixture may be distilled, whereupon the polymer will remain asresidue in the distillation vessel. In some cases the polymer will beprecipitated from the solution and can be filtered off.

The invention is illustrated by the following examples, althoughvariations of the method will be obvious: 1

Example 1 Forty cubic centimeters of a one-normal sodium naphthalenesolution are prepared by the reaction of 1.0 gm. of sodium and 5.0 gms.naphthalene in 35 cc. of dimethylglycol ether. The solution is thenplaced in a 500 cc. capacity three-necked flask in which a nitrogenatmosphere is maintained. This flask is also equipped with an electricagitator and a dropping funnel is inserted through one of its necks. Thesodium naphthalene solution is cooled to -30C., and 100 gms. of1,2-dihydronaphthalene is added through the dropping funnel at a rateconsistent with maintaining the reaction temperature at the aforesaidvalue of 30 C. Water is now dropped into the reaction mixture until thecolored sodium compound is destroyed. 'The precipitated polymer isfiltered off, washed with pure dimethylglycol ether, then with water andfinally dried in an oven or vacuum desiccator. The yield of polymer is90% of the theory or better.

The polymer obtained by this procedure has the appearance of a whiteamorphous powder which is substantially insoluble in all commonsolvents, including aliphatic and aromatic hydrocarbons, water andaliphatic alcohols. In high-boiling chlorinated hydrocarbon solvents itdissolves to some extent to form colloidal solutions. It issubstantially infusible below decomposition temperatures, since whenheated it does not melt at temperatures of 300 C., or below; at highertemperatures it softens and chars at the same time, but this does nottake place until temperatures slightly below red heat have beenattained. The solubility of polymer of 1,2-dihydronaphthalene H;' Sfll0h solvents as alpha-chloronaphthalene' ,fpirn colloidal solutionsvaries with the temperature at which the dihydronaphthalene has beenpolymerized. Polymer prepared at approx. 65 C., dissolves to the extentof about 1.36 gms. per 10 cc. of chloronaphthalene, and the solutiongels on cooling. If this polymer is prepared at 30 C. as abovedescribed, it dissolves only to the extent of about 0.25 gm. per 10 cc.of chloronaphthalene.

Example 2 Twenty grams of styrene and 10 cc. dimethyl glycol other isplaced in a small flask equipped with an agitator and in which anitrogen atmosphere is maintained. With constant stirring and cooling,10 cc. of normal sodium naphthalene solution is gradually added to thestyrene solution. Polymerization takes place with the evolution ofconsiderable heat. Ten cubic centimeters of normal, sodium naphthalenesolution contains 0.23 gram of sodium in the form of the sodium additioncompound. A little water is added to the polymerization mixture tobleach the sodium compounds and carbon dioxide then is passed throughthe liquid to carboxylate the alkali. The carbonate is then filtered offand the ether solvent distilled from the resin; A yield of 19 grams ofpolymer is obtained.

Part of the solvent may be recovered from the ether solution of thealkali metal hydrocarbon compound before using the compound aspolymerizing agent, in order to avoid loss of the solvent ether. Itshould be mentioned that if the solvent is completely distilled off, thealkali metal compound will decompose to form a mixture of aromatichydrocarbon and a colloidal form of the metal. Such mixture willfunction only as an active form of alkali metal. I prefer to avoid theformation of substantial amounts of free metal in my polymerizing agentand I have found that such decomposition may be prevented by leaving inthe mixture a small amount of the solvent, e. g. an amount equal toabout 20% by weight or more of the alkali metal-hydrocarbon compound.

The various polycyclic aromatic hydrocarbons other than naphthalene maybe reacted with sodium or other alkali metal (e. g., potassium orlithium) by the method described herein and the resulting alkali metaladdition compounds may be used to polymerize unsaturated hydrocarbons inaccordance with my herein described invention. Examples of polycyclicaromatic hydrocarbons which may be used in place of naphthalene in myinvention are: diphenyl, di-

naphthyl, anthracene, acenaphthene, phenanthrene, methyl naphthalene andretene.

I claim: a

1. A process for polymerizing styrene comprising contacting styrene withan addition compound of an alkali metal and a polycyclic aromatichydrocarbon, said compound consisting 01 one mol of said hydrocarbonchemically combined with two atoms of said alkali metal.

2. A process for polymerizing styrene comprising contacting styrene withthe sodium addition compoundof naphthalene, which compound may berepresented by the formula CioHaNaz.

NORMAN D. SCOTT.

